In the Southern Hemisphere, many areas are seeing their worst floods in decades. Mudslides and flooding in Brazil have killed at least 479 people this week, while floods in eastern Sri Lanka killed 27.

A resident is seen after a landslide in Teresopolis, Brazil, on Friday. ((Bruno Domingos/Reuters))

Severe floods have also swamped much of northeastern Australia in recent weeks, killing 26 people, leaving 53 missing and affecting hundreds of thousands of people, including residents of Australia's third-largest city, Brisbane.

The heavy rainfall in Australia is a direct result of La Nina's effect on Pacific trade winds, NASA reported this week. The U.S. space agency's satellites confirmed that the current La Nina event is one of the strongest in 50 years.

CBC News meteorologist Natasha Ramsahai said extreme weather in any area bordering the Pacific can "definitely" be related to La Nina.

"The effects of the Pacific Ocean will gradually diminish as you head out geographically from it," she added.

Brazil is on the Atlantic side of South America, making a link between its disastrous floods and La Nina more difficult.

The heavy rainfall in northeastern Australia that led to extreme flooding is a direct result of La Nina's effect on Pacific trade winds, NASA says. ((Reuters))

"Brazil is into their summer monsoon season. Is La Nina enhancing that? The records don't go back far enough for us to say," Ramsahai said.

Other areas bordering the Atlantic have seen unusual weather. Heavy snowfall and cold temperatures have hit northeastern North America, and similar conditions led to hundreds of flight disruptions in Europe before Christmas.

Meanwhile, Nunavut and other areas of the eastern Arctic have seen mild weather.

Lots of unknowns

Ramsahai credits the North Atlantic oscillation, a pattern of weather anomalies that is in its "negative" phase right now.

"How is the North Atlantic oscillation interacting with La Nina, both being very strong this year? That is very low in terms of research and the data that we have," Ramsahai said. "So it's very difficult for us to make definitive answers when our research just isn't there yet."

As of early January, the areas affected by La Nina were 1.5 degrees cooler than normal, reported the U.S. National Oceanic and Atmospheric Administration.

"La Nina is currently near its peak and is expected to persist into the Northern Hemisphere spring 2011 at a lesser intensity," said an update from the agency in a Jan. 6 update. However, it wasn't clear whether the event would last into summer.